An electrographic printing process wherein a magnetically responsive electrically conductive toner material is deposited directly on a dielectric receiver as a result of electronic current flow from an array of magnetically permeable styli into toner chains formed at the tips of the styli is disclosed in an article entitled "Magnetic Stylus Recording" by A. R. Kotz, Journal of Applied Photographic Engineering 7:44-49 (1981).
The toner material described by Kotz is a single-component, magnetically responsive, electrically conductive toner powder, as distinguished from multiple-component carrier/toner mixtures also used in electrophotographic development systems. The magnetically permeable styli described by Kotz are a linear array of magnetically permeable wires potted in a suitable material and arranged such that the ends of the wires are perpendicular to the receiver surface. A major advantage of this system is that it operates in response to relatively low voltage control signals (of the order of 10 volts), thereby allowing direct operation from inexpensive integrated circuits.
One shortcoming of the printing process described by Kotz is that single-component magnetically conductive toners have a limited color gamut (black and brown) and therefor are not suitable for making color images. It would be desirable to make a full color printer using an electrographic printing technique.